- Founding Year: 3082 (2238 as Republic of Marik)
- Capital (City, World): Dormuth, Marik
- National Symbol: a black eagle and banner before a golden disc and purple rectangle
- Location (Terra relative): Rimward-antispinward of Terra, interior
- Total (Inhabited) Systems: 31
- Estimated Population (3130): 91,200,000,000
- Government: Parliamentary Democracy (operating under military rule)
- Ruler: Captain-General Anson Marik
- Dominant Language(s): English (official), Slovak, Czech, Romanian
- Dominant Religion(s): Judaism, Islam, Christianity (Orthodox)
- Unit of Currency: Eagle (1 eagle = 0.52 C-Bills)
The Marik-Stewart Commonwealth was one of the successor states to the late Free Worlds League. The nation constitutes the core of what was once the League, including the capital of Atreus. Ironically, Stewart became a part of the Republic of the Sphere. Though the League finally collapsed in 3078, Corinne Marik did not take upon herself the mantle of the Captain-General until 3082. The Marik-Stewart Commonwealth is essentially a fusion of the Marik Commonwealth and the Stewart Commonality, though it also includes some portions of the Silver Hawks Coalition.
The Republic of the Sphere viewed the nascent Marik-Stewart Commonwealth as the greatest threat to the Republic within the boundaries of the former Free Worlds League, as the Army of the Marik Commonwealth (later the Army of the Marik-Stewart Commonwealth) was rebuilding quickly with combat-experienced troops while Corinne Marik pressed her claim to such worlds as Kalidasa and Stewart, one occupied by the Gryphons and the other the Stewart Dragoons with each proving distinctly unwilling to relinquish them to the Republic.
Corrine's grandson, Anson Marik, attempted to take Stewart from the Republic in 3134, but his invasion failed. He moved the capital from Marik to Atreus in 3136 under threat of invasion from the Lyran Commonwealth. This move proved fortuitous when the Oriente Protectorate launched an invasion of its own soon after that led to the seizure of Marik. Anson also resurrected the Silver Hawk Irregulars, a military force that had been shattered during the Jihad to combat the Lyran invasion when it finally materialized. Coupled with a high-ranking spy, the Commonwealth has so far been able to survive against its larger neighbor.
In August 3137, the Lyran Commonwealth and Clan Wolf invaded the Commonwealth. The Silver Hawk Irregulars began a guerilla warfare campaign against the Lyran incursion which lasted until the Irregulars were effectively wiped-out by the combined Lyran and Clan Wolf forces on Helm. Only 50 to 100 members survived what became known as the Helm Massacre.
On June 5th, 3138 the Lyran & Clan Wolf expedition invaded Stewart. Anson Marik ordered the remaining members of the Silver Hawk Irregulars off-planet to prevent their destruction. Anson was later killed in a running gun battle with Lyran forces in his stronghold.
With no heir to be found and no contingency plans, the Marik-Stewart Commonwealth was decapitated and de facto destroyed by the invasion. It's highly likely that most of its worlds and surviving military units joined the ressurected Free Worlds League pledging their alliegance to Jessica Marik.